The invention relates generally to assembly of exhaust treatment devices, such as catalytic converters. More specifically, the invention concerns substrate insertion apparatus utilizing a compressed fluid bearing.
Gas, e.g., exhaust gas, treatment devices such as catalytic converters, evaporative emission devices, scrubbing devices, diesel particulate traps, and the like are employed in various applications to physically and/or catalytically treat environmentally unfriendly gas emission. Such gas treatment devices typically incorporate a substrate or brick which includes catalyst coating. A mounting device such as a support mat comprising a compressible material is typically disposed about the substrate forming a mat support material/substrate subassembly prior to being inserted into a housing compartment of the gas treatment device.
One conventional method for inserting a mat/substrate combination into the housing compartment comprises using a stuffing cone, such as disclosed in U.S. Pat. Nos. 6,532,659 and 6,732,432. With devices as shown in these patents, an outlet of the stuffing cone is disposed adjacent to an inlet or opening of the housing compartment. The cone structure has an inner diameter less than the inner diameter of the housing compartment. As the mat/substrate combination moves through the stuffing cone toward the housing compartment, the cone compresses the compressible mat about the substrate so that the subassembly can be disposed into the housing compartment. As the mat/substrate combination slides against the inwardly tapered interior of the stuffing cone, the mat compresses about the substrate until the combination has an outer diameter less than the outer diameter of the housing compartment opening. At this point, the combination is pushed or stuffed into the exhaust treatment device housing.
During this conventional stuffing cone process, the support mat performance is degraded (i.e., its holding forces are reduced) as a result of shear damage to the mat material during the stuffing process. This shear damage is caused principally by the pulling/pushing of the mat during compression and friction between the mat and the stuffing device.
The relationship between stuffing speed and radial compression speed of the mat is fixed by the stuffing cone geometry and cannot be varied independently. The mat is dragged into the narrowing frustoconical device and is therefore subjected to tensile elongation and shear damage. The tensile elongation results in a reduced gap bulk density of the mat and fiber breakage. A coefficient of friction between the stuffing cone and the compressible mat cannot be effectively improved. Films, coatings or lubricant have been employed to reduce friction but have a decidedly negative impact on mat in-service performance.
Hence, there is seen to be a need in the pertinent art for a mat/substrate stuffing or insertion mechanism which minimizes shear damage to the compressible mat by, in turn, minimizing a coefficient of friction between the mat and the insertion device during the stuffing process and independently permitting optimization of compression speed.